1. Industrial application field
The present invention relates to a collet chuck for mounting a tool such as drill, end mill and the like to a rotary spindle in various kinds of machine tools.
2. Prior art
The collet chuck which has been conventionally used comprises a main body of a chuck having a tapered hole at its top end part, a collet having a tapered surface which is detachably fitted into the tapered hole at its external periphery, and a fastening nut which is fitted around the collet and, at the same time, is detachably screwed on the main body of the chuck, wherein the collet is adapted to be reduced in its diameter by axially elongated slots provided in the collet alternately from both the sides including its top end side and its rear end side, and a fastening operation of the fastening nut allows the collet not only to be fitted into the taper hole in a pressable manner but also to be reduced in its diameter, thereby fastening and fixing the tool which is fitted into the collet in an insertional manner. As the prior art of FIG. 11 shows, while an annular groove 2 is provided around the external periphery on the top end side of the collet 1 and an outward flange 3 is formed on the top end part of the collet 1, an inward flange 5 is formed around the internal periphery of the fastening nut 4, and, consequently, such a filling of the inward flange 5 into the annular groove 2 as shown by a dashed line of the same figure permits the collet 1 and the fastening nut 4 to be detachably connected to each other.
The collet 1 is fitted into the taper hole of the main body of the chuck and the pressing or drawing action of the fastening nut 4 causes the collet 1 to be mounted to or detached from the tapered hole.
Since the tool capable of being mounted by way of the collet into the main body of the chuck is limited to the one whose diameter of a shaft to be mounted therein is adequately adaptable to the possible scope of reducing the internal diameter of the collet by fastening the collet with the fastening nut, if there is a change between the tools to be mounted into the main body of the chuck, which have a remarkable difference in the diameter of their shafts to be mounted therein, there is a necessity of making a replacement with the collet whose internal diameter is equally corresponding to such a change. In that case, in order to mount or detach the collet 1 to or from the fastening nut 4, the prior art of FIG. 11 requires the collet 1 to be entirely reduced in its diameter at least to the extent of the difference in diameter S1 between the maximum external diameter d1 of the outward flange 3 and the internal diameter D1 of the inward flange 5. But, since the necessity of providing a margin to be held between both the flanges 3 & 5 even in the case where the diameter of the collet 1 is minimumized so that the collet 1 may be drawn out from the main body of the chuck, while the collet 1 is being accompanied with the fastening nut 4 in a pulling manner, the difference in diameter S1 is defined to a considerably long extent. The mounting or detaching of the collet 1 to or from the fastening nut 4 may need an extremely large amount force for the reduction of the diameter so that there is a difficulty in replacing only the collet in the process of the exchange between the tools.